一、避孕套其原理为不让精子进入阴道,主要是隔离作用。二、阴道隔膜使精子不能进入宫腔。三、外用避孕药以杀精或改变精子功能达到避孕。上述三种方法正确使用,避孕率几乎可达100％,但事实上,意外怀孕的事件仍有发生。原因是: 1.性交中途才使用在性交中途才使用避孕套,导致怀孕的危险率之高与阴道外射精几乎没 First, the principle of condoms to prevent sperm into the vagina, the main role of isolation. Second, the vaginal diaphragm so that sperm can not enter the uterine cavity. Third, topical contraceptives to kill or change sperm function to achieve contraception. Proper use of the above three methods, contraception rate is almost 100%, but in fact, unplanned pregnancy events still occur. The reasons are: 1. Used only halfway through sexual intercourse before the use of condoms, leading to high risk of pregnancy and vaginal ejaculation almost no